Internal combustion engines may utilize direct fuel injection, wherein fuel is directly injected in to an engine cylinder, to improve fuel gas mixing. In traditional direct fuel injectors, the injector nozzle hole configuration and geometry can regulate combustion characteristics and effect vehicle emissions. The fuel is typically injected from a sac at the tip of the fuel injector needle into the engine cylinder through a plurality of holes, configured in various forms to increase atomization and improve air-fuel mixing.
One example approach for improving air-fuel mixing with a direct injector is shown by Abani et al. in WO2014052126. Therein, an injector nozzle comprises a plurality of holes skewed with respect to the axis of the injector in order to impart an angular momentum on a plume of injected fuel.
However, the inventors herein have recognized some issues with the above fuel injector. For example, because the fuel is ejected out of the nozzle at high pressure, the fuel may have a relatively long spray penetration, despite the swirl imparted by the skewed nozzle holes. As a result, the fuel may impinge upon the cylinder walls. Particularly during cold engine conditions, the fuel on the cylinder wall may not participate in combustion, leading to fueling errors and compromising emissions. In another example, the sac at the base of the injector needle is in communication with the cylinder through the nozzle holes even after the injector is in a closed position. The residual volume of fuel from the sac can thus drip into the cylinder after the injector is closed, which may result in injector coking. This can degrade fuel spray pattern and vehicle emissions. Prolonged buildup due to fuel dripping can also decrease the effective flow area of the nozzle holes, decreasing the efficiency of fuel injection, and consequently, a reduction in engine power and/or torque may be observed.
Thus, a fuel injector is presented herein to at least partly address the above issues. In one example, the fuel injector comprises a needle and a frustum shaped nozzle end coupled to the needle. In this way, the fuel may travel over the frustum-shaped nozzle end when the fuel is injected out of the injector, atomizing the fuel to promote mixing and imparting rotational momentum to the fuel spray.
In one example, the nozzle end of the needle may include a plurality of tangential fins positioned on an outer surface of the frustum. Further, the tangential fins may be curved, for example in a counter-clockwise direction. To inject fuel, the needle may be moved outward, away from the center of the injector and into a cylinder to which the fuel injector is coupled. In this way, an annulus nozzle may be created between a body of the injector housing the needle and the frustum-shaped nozzle end of the needle. The fuel flowing out of the injector travels over the frustum-shaped nozzle end and curved tangential fins. In doing so, fuel is injected with a cone shaped-spray and a swirl motion may be imparted to the fuel spray via the curved fins, thus reducing the spray penetration and cylinder wall wetting. Further, air-fuel mixing may be increased.
In another embodiment, the fuel injector may have two injector needles, a primary injector needle and a secondary injector needle, where the secondary injector needle is coupled to the frustum shaped nozzle end. A fuel chamber (e.g., sac) may be located in a space between the primary needle and the secondary needle. An electric actuator may be used to move the primary injector needle to establish fluidic communication between a fuel passage and the fuel chamber. Once sufficient pressure is reached in the fuel chamber, the secondary needle may be actuated via the fuel pressure to create the annulus nozzle over which the fuel travels to the cylinder. In another embodiment of the fuel injector, the secondary injector needle nozzle end may have a plurality of curved fins on its surface. The curved fins may provide rotational momentum to the injector nozzle to reduce fuel penetration and increase air-fuel mixing.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.